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Diffstat (limited to 'Documentation/connector/connector.txt')
| -rw-r--r-- | Documentation/connector/connector.txt | 196 |
1 files changed, 0 insertions, 196 deletions
diff --git a/Documentation/connector/connector.txt b/Documentation/connector/connector.txt deleted file mode 100644 index ab7ca897fab7..000000000000 --- a/Documentation/connector/connector.txt +++ /dev/null @@ -1,196 +0,0 @@ -/*****************************************/ -Kernel Connector. -/*****************************************/ - -Kernel connector - new netlink based userspace <-> kernel space easy -to use communication module. - -The Connector driver makes it easy to connect various agents using a -netlink based network. One must register a callback and an identifier. -When the driver receives a special netlink message with the appropriate -identifier, the appropriate callback will be called. - -From the userspace point of view it's quite straightforward: - - socket(); - bind(); - send(); - recv(); - -But if kernelspace wants to use the full power of such connections, the -driver writer must create special sockets, must know about struct sk_buff -handling, etc... The Connector driver allows any kernelspace agents to use -netlink based networking for inter-process communication in a significantly -easier way: - -int cn_add_callback(struct cb_id *id, char *name, void (*callback) (struct cn_msg *, struct netlink_skb_parms *)); -void cn_netlink_send_multi(struct cn_msg *msg, u16 len, u32 portid, u32 __group, int gfp_mask); -void cn_netlink_send(struct cn_msg *msg, u32 portid, u32 __group, int gfp_mask); - -struct cb_id -{ - __u32 idx; - __u32 val; -}; - -idx and val are unique identifiers which must be registered in the -connector.h header for in-kernel usage. void (*callback) (void *) is a -callback function which will be called when a message with above idx.val -is received by the connector core. The argument for that function must -be dereferenced to struct cn_msg *. - -struct cn_msg -{ - struct cb_id id; - - __u32 seq; - __u32 ack; - - __u32 len; /* Length of the following data */ - __u8 data[0]; -}; - -/*****************************************/ -Connector interfaces. -/*****************************************/ - -int cn_add_callback(struct cb_id *id, char *name, void (*callback) (struct cn_msg *, struct netlink_skb_parms *)); - - Registers new callback with connector core. - - struct cb_id *id - unique connector's user identifier. - It must be registered in connector.h for legal in-kernel users. - char *name - connector's callback symbolic name. - void (*callback) (struct cn..) - connector's callback. - cn_msg and the sender's credentials - - -void cn_del_callback(struct cb_id *id); - - Unregisters new callback with connector core. - - struct cb_id *id - unique connector's user identifier. - - -int cn_netlink_send_multi(struct cn_msg *msg, u16 len, u32 portid, u32 __groups, int gfp_mask); -int cn_netlink_send(struct cn_msg *msg, u32 portid, u32 __groups, int gfp_mask); - - Sends message to the specified groups. It can be safely called from - softirq context, but may silently fail under strong memory pressure. - If there are no listeners for given group -ESRCH can be returned. - - struct cn_msg * - message header(with attached data). - u16 len - for *_multi multiple cn_msg messages can be sent - u32 port - destination port. - If non-zero the message will be sent to the - given port, which should be set to the - original sender. - u32 __group - destination group. - If port and __group is zero, then appropriate group will - be searched through all registered connector users, - and message will be delivered to the group which was - created for user with the same ID as in msg. - If __group is not zero, then message will be delivered - to the specified group. - int gfp_mask - GFP mask. - - Note: When registering new callback user, connector core assigns - netlink group to the user which is equal to its id.idx. - -/*****************************************/ -Protocol description. -/*****************************************/ - -The current framework offers a transport layer with fixed headers. The -recommended protocol which uses such a header is as following: - -msg->seq and msg->ack are used to determine message genealogy. When -someone sends a message, they use a locally unique sequence and random -acknowledge number. The sequence number may be copied into -nlmsghdr->nlmsg_seq too. - -The sequence number is incremented with each message sent. - -If you expect a reply to the message, then the sequence number in the -received message MUST be the same as in the original message, and the -acknowledge number MUST be the same + 1. - -If we receive a message and its sequence number is not equal to one we -are expecting, then it is a new message. If we receive a message and -its sequence number is the same as one we are expecting, but its -acknowledge is not equal to the sequence number in the original -message + 1, then it is a new message. - -Obviously, the protocol header contains the above id. - -The connector allows event notification in the following form: kernel -driver or userspace process can ask connector to notify it when -selected ids will be turned on or off (registered or unregistered its -callback). It is done by sending a special command to the connector -driver (it also registers itself with id={-1, -1}). - -As example of this usage can be found in the cn_test.c module which -uses the connector to request notification and to send messages. - -/*****************************************/ -Reliability. -/*****************************************/ - -Netlink itself is not a reliable protocol. That means that messages can -be lost due to memory pressure or process' receiving queue overflowed, -so caller is warned that it must be prepared. That is why the struct -cn_msg [main connector's message header] contains u32 seq and u32 ack -fields. - -/*****************************************/ -Userspace usage. -/*****************************************/ - -2.6.14 has a new netlink socket implementation, which by default does not -allow people to send data to netlink groups other than 1. -So, if you wish to use a netlink socket (for example using connector) -with a different group number, the userspace application must subscribe to -that group first. It can be achieved by the following pseudocode: - -s = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR); - -l_local.nl_family = AF_NETLINK; -l_local.nl_groups = 12345; -l_local.nl_pid = 0; - -if (bind(s, (struct sockaddr *)&l_local, sizeof(struct sockaddr_nl)) == -1) { - perror("bind"); - close(s); - return -1; -} - -{ - int on = l_local.nl_groups; - setsockopt(s, 270, 1, &on, sizeof(on)); -} - -Where 270 above is SOL_NETLINK, and 1 is a NETLINK_ADD_MEMBERSHIP socket -option. To drop a multicast subscription, one should call the above socket -option with the NETLINK_DROP_MEMBERSHIP parameter which is defined as 0. - -2.6.14 netlink code only allows to select a group which is less or equal to -the maximum group number, which is used at netlink_kernel_create() time. -In case of connector it is CN_NETLINK_USERS + 0xf, so if you want to use -group number 12345, you must increment CN_NETLINK_USERS to that number. -Additional 0xf numbers are allocated to be used by non-in-kernel users. - -Due to this limitation, group 0xffffffff does not work now, so one can -not use add/remove connector's group notifications, but as far as I know, -only cn_test.c test module used it. - -Some work in netlink area is still being done, so things can be changed in -2.6.15 timeframe, if it will happen, documentation will be updated for that -kernel. - -/*****************************************/ -Code samples -/*****************************************/ - -Sample code for a connector test module and user space can be found -in samples/connector/. To build this code, enable CONFIG_CONNECTOR -and CONFIG_SAMPLES. |